As Fathom pointed out, this is most likely a result of link equity coming into the site, which impacts a site's available crawl budget. Less link equity = smaller crawl budget. Still, there are strategies to maximize available crawl budget, such as:

1) Disallowing non-revenue generating pages (like About Us, Privacy Policy, Shipping and Returns, Careers, etc) from being crawled via robots.txt or meta=robots markup (Noindex, follow)
2) Updating internal links so search engine bots don't have to go through redirects, stacked redirects or end up on 404 pages.
3) Assigning Priorities to URLs in XML Sitemaps based on their importance to the site/business; also, assigning Frequencies to indicate pages that do and don't change that often
4) Minimizing code "bloat", including inline CSS and JavaScript
5) Etc